Feedback interval control

Abstract

A multiple-input multiple-output (MIMO) wireless communication systems that includes a plurality of adjacent cells, each containing one or more base stations operable to transmit signals to, and receive signals transmitted from, one or more users. The users are operable to feed back to the relevant base station(s) channel state information relating to channel(s) between the relevant base station(s) and the users, and the base stations are operable to adapt signals for transmission to users, based on the fed back channel state information, to account for channel variations. The proposed method involves obtaining information related to time-variation in channel spatial structure, and adjusting the timing with which a user feeds back channel state information, based on the time variation in channel spatial structure. The invention helps to achieve a suitable balance between the feedback overhead and system performance, and may be operable in systems operating according to various CoMP transmission modes.

Description

[0001]This is a continuation of Application PCT / EP2010 / 070315, filed Dec. 20, 2010, now pending, which claims priority from the European Patent Application No. 09180243.9, filed Dec. 21, 2009, the contents of each are herein wholly incorporated by reference.[0002]The present invention relates to wireless communication systems, and in particular to multi-cell multiple-input multiple-output (“MIMO”) systems in which there is coordination of transmissions between cells. It is envisaged that the invention may be implemented in systems compliant with the 3GPP LTE, 3GPP LTE-A, IEEE 802.16 and 802.11 groups of standards, however it is to be clearly understood that these are merely examples, and the invention could equally be implemented in any other form of multi-cell MIMO system.UNDERLYING TECHNOLOGY[0003]This section gives an introductory overview to certain relevant technologies and principles involved in the field to which the present invention relates, and helps to provide context for...

AI Technical Summary

Benefits of technology

The patent text describes a method for adapting signals sent to user equipment based on feedback from the relevant base station about the state of the communication channel. The feedback is determined based on the time variation characteristics of the MIMO channel, which helps to maintain accurate and relevant information for effective link adaptation. The method allows for a balance to be achieved between the feedback overhead and system performance, regardless of the speed at which the MIMO channel changes. This results in faster and more efficient communication between the base station and user equipment.

Problems solved by technology

However, in the more elaborate multi-cellular networks discussed in the previous paragraph, the benefits of OFDMA and MIMO transmission can often be limited by inter-cell interference.

Inter-cell interference may arise, for example, because the frequency resources (i.e. the carriers and subcarriers) utilised by base stations in transmitting data to users in one cell are identical to the frequency resources utilised by base stations in transmitting data to users in an adjacent cell.

And because common frequency resources are used in adjacent cells (i.e. there is simultaneous use of substantially identical transmission frequencies in adjacent cells), signals being transmitted in the adjacent cells can often interfere with data being transmitted to the cell-edge user.

However, the trade-off for this improvement is that the coordination of transmissions in multi-cellular MIMO systems requires channel state information (CSI) and data information to be shared among the coordinated base stations.

This in turn results in a significant additional burden on the system's transmission and data capacity resources.

As also explained above, for FDD systems, the amount of channel information needed to be fed back increases linearly with the number of cooperating cells (or sectors of cells), and this creates a heavy additional burden for the uplink channel particularly.

Furthermore, high performance CoMP transmission schemes are often very sensitive to channel information being outdated.

Therefore, the benefits of CoMP may diminish, or may not be as realisable, in high mobility scenarios such as, for example, where UE velocities are 120 km / h or higher, since the feedback requirements necessary to enable CoMP to function optimally or well for such high velocities are difficult to satisfy.

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